1. Field of Invention
This invention is related to processes for making bichromal particles for gyricon displays.
2. Description of Related Art
Gyricon displays, also called twisting-ball displays, rotary ball displays, particle displays, dipolar particle light valves, etc., offer a technology for making a form of electric paper. Gyricon displays are addressable displays including a plurality of optically anisotropic balls, each of which can be selectively rotated to orient a desired surface for viewing by an observer. For example, gyricon displays can incorporate balls each having two distinct hemispheres, one black and the other white, with each hemisphere having a distinct electrical characteristic (e.g., zeta potential with respect to a dielectric fluid) so that the balls are electrically as well as optically anisotropic. Other kinds of rotating elements are also known. For example, U.S. Pat. No. 4,261,653, which is incorporated herein by reference in its entirety, discloses a multilayer sphere, although it is made at least in part from glass and its use depends on an addressing scheme involving high-frequency electric fields.
In known gyricon displays, the black-and-white balls are embedded in a sheet of optically transparent material, such as an elastomer layer, which contains spheroidal cavities and is permeated by a transparent dielectric fluid, such as a plasticizer. The fluid-filled cavities are sized to accommodate the balls, one ball per cavity, so as to prevent the balls from migrating within the sheet. The balls can be selectively rotated within their respective fluid-filled cavities, for example by application of an electric field, so as to present either the black or the white hemisphere to observers viewing the surface of the sheet. Thus, by application of an electric field that is addressable in two dimensions (as by a matrix addressing scheme), the black and white sides of the balls can be caused to appear as the image elements (e.g., pixels or subpixels) of a displayed image.
U.S. Pat. No. 5,389,945, incorporated herein by reference in its entirety, shows that gyricon displays can be made that have many of the desirable qualities of paper, such as flexibility and stable retention of a displayed image in the absence of power, not found in conventional display media. Gyricon displays can also be made that are not paper-like, for example, in the form of rigid display screens for flat-panel displays.
Gyricon displays are also disclosed in U.S. Pat. Nos. 5,262,098; 5,344,594; 5,717,514; 5,989,629 and 6,097,531, each incorporated herein by reference in its entirety.
This invention provides in-situ processes for making bichromal particles.
This invention also separately provides gyricon sheets and gyricon displays comprising the bichromal particles.
Exemplary embodiments of the in-situ processes for making bichromal particles according to this invention comprise forming first particles having a first color and an anionic surface charge, and separately forming second particles having a second color and a cationic surface charge. The first particles and second particles are mixed and aggregated to form bichromal aggregates. The aggregated first particles and second particles are coalesced to form bichromal particles that comprise one first particle and one second particle.
Exemplary embodiments of the processes for making gyricon sheets according to the invention comprise placing the bichromal particles in cavities of a transparent optical medium, which contain a transparent dielectric fluid, such that a single one of the bichromal particles is each cavity.
Exemplary embodiments of the processes for making gyricon displays according to the invention comprise placing a gyricon sheet between opposed substrates.